The matrix \(M=\left[\begin{array}{cc}\cos \alpha & \sin \alpha \\ i \sin \alpha & i \cos \alpha\end{array}\right] \) is a unitary matrix when α is
1
\((2 n+1) \frac{\pi}{2}, n \in \mathbb{Z} \)
2
\((3 n+1) \frac{\pi}{3}, n \in \mathbb{Z} \)
3
\((4 n+1) \frac{\pi}{4}, n \in \mathbb{Z}\)
4
More than one of the above
5
None of the above